How to refactor, (shorten) this query - mysql

Question

I have a database with tables: applicant (or candidate for a job), application (candidate applied for a certain job), test, selected_test(any application has a defined set of tests) and test_result.
When I need to show which applicant scored what result for any application and test I would use this query:
SELECT applicant.first_name, applicant.last_name, application.job, test.name, test_result.score
FROM applicant
INNER JOIN application ON application.applicant_id=applicant.id
INNER JOIN selected_test ON application.id=selected_test.application_id
INNER JOIN test ON selected_test.test_id=test.id
INNER JOIN test_result ON selected_test.test_id=test_result.test_id AND applicant.id=test_result.applicant_id
What I need to accomplish is sorting by certain test type (test.name) along with test.score
This is what I mean:
SELECT a.first_name, a.last_name, app.job, iq.score AS iqScore, math.score AS mathScore, personality.score AS personalityScore, logic.score AS logicScore
FROM applicant a
INNER JOIN application app ON a.id=app.applicant_id
LEFT JOIN
(SELECT app.id AS appId, tr.score
FROM applicant a
INNER JOIN application app ON app.applicant_id=a.id
INNER JOIN selected_test st ON app.id=st.application_id
INNER JOIN test t ON st.test_id=t.id AND t.name='iq'
INNER JOIN test_result tr ON st.test_id=tr.test_id AND a.id=tr.applicant_id) AS iq ON app.id=iq.appId
LEFT JOIN
(SELECT app.id AS appId, tr.score
FROM applicant a
INNER JOIN application app ON app.applicant_id=a.id
INNER JOIN selected_test st ON app.id=st.application_id
INNER JOIN test t ON st.test_id=t.id AND t.name='math'
INNER JOIN test_result tr ON st.test_id=tr.test_id AND a.id=tr.applicant_id) AS math ON app.id=math.appId
LEFT JOIN
(SELECT app.id AS appId, tr.score
FROM applicant a
INNER JOIN application app ON app.applicant_id=a.id
INNER JOIN selected_test st ON app.id=st.application_id
INNER JOIN test t ON st.test_id=t.id AND t.name='personality'
INNER JOIN test_result tr ON st.test_id=tr.test_id AND a.id=tr.applicant_id) AS personality ON app.id=personality.appId
LEFT JOIN
(SELECT app.id AS appId, tr.score
FROM applicant a
INNER JOIN application app ON app.applicant_id=a.id
INNER JOIN selected_test st ON app.id=st.application_id
INNER JOIN test t ON st.test_id=t.id AND t.name='logic'
INNER JOIN test_result tr ON st.test_id=tr.test_id AND a.id=tr.applicant_id) AS logic ON app.id=logic.appId
ORDER BY mathScore DESC, iqScore DESC, logicScore DESC
The query returns a set of applications, showing applicant data, job, test names and scores.
For instance, if I want candidate applications with higher "math" score, followed by highest scores in "IQ" and then in "logic" to be on top, 'ORDER BY' clause looks like the above.
The query works correct but the problem is that in real situation it deals with large data sets and I need a way to shorten/refactor this query.
Example database it works on is here:
CREATE TABLE IF NOT EXISTS `applicant` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`first_name` varchar(255) NOT NULL,
`last_name` varchar(255) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=8 ;
--
-- Dumping data for table `applicant`
--
INSERT INTO `applicant` (`id`, `first_name`, `last_name`) VALUES
(2, 'Jack', 'Redburn'),
(4, 'Barry', 'Leon'),
(6, 'Elisabeth', 'Logan'),
(7, 'Jane', 'Doe');
-- --------------------------------------------------------
--
-- Table structure for table `application`
--
CREATE TABLE IF NOT EXISTS `application` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`applicant_id` int(11) NOT NULL,
`job` varchar(255) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=10 ;
--
-- Dumping data for table `application`
--
INSERT INTO `application` (`id`, `applicant_id`, `job`) VALUES
(2, 2, 'Salesman'),
(4, 4, 'Policeman'),
(6, 6, 'Journalist'),
(8, 6, 'Hostess'),
(9, 7, 'Journalist');
-- --------------------------------------------------------
--
-- Table structure for table `selected_test`
--
CREATE TABLE IF NOT EXISTS `selected_test` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`application_id` int(11) NOT NULL,
`test_id` int(11) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=24 ;
--
-- Dumping data for table `selected_test`
--
INSERT INTO `selected_test` (`id`, `application_id`, `test_id`) VALUES
(1, 1, 1),
(2, 1, 2),
(3, 1, 3),
(5, 2, 1),
(6, 2, 2),
(7, 2, 3),
(8, 2, 4),
(9, 3, 4),
(10, 3, 2),
(11, 4, 1),
(12, 4, 2),
(13, 4, 3),
(14, 4, 4),
(15, 5, 2),
(16, 5, 3),
(17, 6, 1),
(18, 6, 4),
(19, 7, 3),
(20, 7, 2),
(21, 7, 1),
(22, 8, 2),
(23, 8, 3);
-- --------------------------------------------------------
--
-- Table structure for table `test`
--
CREATE TABLE IF NOT EXISTS `test` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(255) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=5 ;
--
-- Dumping data for table `test`
--
INSERT INTO `test` (`id`, `name`) VALUES
(1, 'math'),
(2, 'logic'),
(3, 'iq'),
(4, 'personality');
-- --------------------------------------------------------
--
-- Table structure for table `test_result`
--
CREATE TABLE IF NOT EXISTS `test_result` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`applicant_id` int(11) NOT NULL,
`test_id` int(11) NOT NULL,
`score` int(11) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=24 ;
--
-- Dumping data for table `test_result`
--
INSERT INTO `test_result` (`id`, `applicant_id`, `test_id`, `score`) VALUES
(2, 2, 1, 6),
(3, 4, 1, 7),
(6, 6, 1, 3),
(7, 7, 1, 8),
(9, 2, 2, 15),
(11, 4, 2, 12),
(13, 6, 2, 11),
(14, 7, 2, 9),
(15, 7, 3, 105),
(16, 6, 3, 112),
(18, 4, 3, 108),
(20, 2, 3, 117),
(22, 4, 4, 70);
And here is what results look like:
First query is just to show you how data is related:
The large query, shows score data horizontally so it is possible to sort by test name and score:

Answer 1

caveat I don't know mysql
Googling mysql pivot gives this result http://en.wikibooks.org/wiki/MySQL/Pivot_table
So if we apply the same logic using the test.id as the seed number (which is exam in the example from the google search) we get this:
SQLFIDDLE
select first_name, last_name, job,
sum(score*(1-abs(sign(testid-1)))) as math,
sum(score*(1-abs(sign(testid-2)))) as logic,
sum(score*(1-abs(sign(testid-3)))) as iq,
sum(score*(1-abs(sign(testid-4)))) as personality
from
(
SELECT applicant.first_name, applicant.last_name, application.job, test.name, test_result.score, test.id as testid
FROM applicant
INNER JOIN application ON application.applicant_id=applicant.id
INNER JOIN selected_test ON application.id=selected_test.application_id
INNER JOIN test ON selected_test.test_id=test.id
INNER JOIN test_result ON selected_test.test_id=test_result.test_id AND applicant.id=test_result.applicant_id
) t
group by first_name, last_name, job
Now you've got your short query yu can apply sorting as required - you can use case statement in you order by to dynamically change the order as required...

Answer 2

I noticed that you have only defined primary keys. You should see a noticeable performance improvement when you index other fields. Index at least the following: application.applicant_id, selected_test.application_id, selected_test.test_id, test_result.applicant_id, test_result.test_id, test_result.score.
You might be surprised how much this speeds things up for you. In fact, mysql tells us this is the best way to improve performance: https://dev.mysql.com/doc/refman/5.5/en/optimization-indexes.html.